In the petrochemical industry where systems of pipes are used to carry toxic and/or explosive gases or liquids, both scheduled and unscheduled work is periodically required on the pipe system. This work is usually required for maintenance or insurance purposes or to comply with provincial, state or federal laws. When modifications to the piping system, routine maintenance and/or leak repairs are to be performed, this work may require vessel entry for hot work such as torch cutting or welding.
In order to undertake hot work, it is necessary that a particular section of pipe be isolated from adjacent or connecting equipment and completely purged of any potentially explosive material within the pipeline. The isolation and purging procedures are very exacting and require experienced personnel to conduct the work in order to eliminate the risk of explosion and/or damage to the equipment.
In the past, practice has been to isolate and seal a particular section of pipe from the adjacent pipes in the system. Past practice has been to use a steel plate or blind and a number of spacers sandwiched between the steel plate and an adjacent flange which thereby form a series of openings to permit a purging gas to be flushed through the isolated section of pipe. In a typical pipe connection, the connecting pipe sections are bolted together through flanges on each pipe end with a gasket sandwiched between abutting end surfaces. In isolating one section of pipe from the other in order for work to be performed one section of pipe, the flange bolts are loosened and the pipe sections are spread apart using a flange spreading tool. A number of bolts are removed to provide sufficient space to insert a steel plate between the flanges and inside the bolts of adjacent pipe sections. Any gasket between the flanges would normally be retained on the side of the pipe section which is not being worked upon. A number of metal spacers would be placed on the work side of the plate, between the plate and flange thereby creating spaces to allow gases/vapours to escape. The flange bolts are reinserted and all are tightened to create a tight seal and hold all components in place. A similar procedure at the opposite end of the pipe section would create a second space to enable a purging gas to be flushed through the pipe section.
While this procedure can effectively be used to create a safe environment for hot work, a number of problems exist which can lead to unsafe practices and/or damage to equipment. In particular, the use of separate metal spacers requires the handling and positioning of several components, each of which must be accurately placed before tightening of the flange bolts at the time of installing the blind. Each component must also be carefully removed when the blind is removed. In this situation, the opportunity exists, both during placement and removal, for any number of spacers to drop into the pipe necessitating their removal. Removal of dropped spacers is difficult and time-consuming. In situations where it has not been noticed that a spacer has dropped into the pipe, the loose spacer may be trapped within the pipe causing damage elsewhere in the system when flow is resumed in the system. Furthermore, if spacers are of marginally different thickness, the spacer may not be tightly sandwiched between the flanges when the flange bolts are tightened, leading to a situation where the spacer may drop within the pipe or be blown out by the force of the purging medium. Furthermore, in the past, the materials used as spacers have been highly varied and often unsuitable and have included materials such as welding rods, washers, shim metal and even wood. The use of spacers may also contribute to flange and/or gasket damage which then results in a leaking joint when the system is put back in service. Expensive repairs or replacements may be required to correct leaks. Furthermore, in the past, where leaking joints have resulted from a purging operation using spacers, flange bolts are often over-torqued when re-tightened following the purging operation and which may thereafter contribute to a later failure of the bolt.
Accordingly, there has been a need for a purging blind that eliminates the need for spacers by providing a single component design for a purging blind.
Furthermore, when a blind is installed between two pipe sections, it is important that it is axially aligned between the flanges to ensure sufficient overlap between the blind and the inner flange surface. An improperly aligned blind may be subject to loss of seal and result in an explosion hazard. Thus, there has been a need for a purging blind that is self-locating between the pipe-sections to ensure correct axial alignment between the blind and flanges.
Furthermore, there has been a need for a purging blind that can be used in a variety of different sized pipe sections. In that pipes used in the industry generally comply with American National Standards Institute (ANSI) or American Petroleum Institute (API) Specification Tables, there has been a need for a purging blind design that may be used in pipes of different sizes in order to reduce the number of purging blinds which need to be stocked where the design ensures axial alignment of the blind.
Furthermore, there has been a need for a purging blind that is reversible and can be installed for left to right purging or right to left purging as required.
There has also been a need for a device designed for ease of installation and removal, having a one-piece construction with a handle and that is transportable to remote locations including off-shore rigs, if necessary.
Furthermore, in order to simplify the purging process and reduce costs associated with purging, there has been a need for a purging blind that provides a series of blind sizes with channels which enable a consistent purging volume to be expelled where the channel widths varying with blind diameter. Specifically, there has been a need for a device that for a given pressure of purge gas, the flow of that purge gas through the channels of the blind will remain constant through all pipe diameters for more consistent purging which is critical to the safety of personnel and equipment.
Furthermore, there has been a need for a purging blind where the centre-line of one venting channel is offset with respect to the centre line of a handle in order to ensure that the venting blind allows purging gases to exhaust through the channels which are not aligned with any of the flange bolts so as to avoid any possible restriction to the exhaust of the purge gas.
As indicated above, past practice in the industry has been to cut the correct diameter of the blind from carbon steel plate which is then inserted between flanges. One side of the plate is gasketed and spacers are inserted in the other side of the blind in order to create channels for effect purging.
A review of the prior art reveals that the problems discussed above have not been addressed in past devices. For example, U.S. Pat. No. 4,452,278 discloses a spectacle line blind with a vent that enables two sections of pipe to be isolated from another and U.S. Pat. 2,726,683 discloses a spectacle blind which also enables two sections of pipe to be isolated from one another. These patents do not, however, disclose a venting blind for use with flanged pipe sections that could be implemented without structural changes to the piping system.